The present invention relates to a power-line communication method, a power-line communication device, and a power-line communication system, which make multi-carrier communication using a power line as a communication medium.
It is known that noises synchronized with an AC power source cycle exist in a power line. Accordingly, when communication is made using a power line as a communication medium, efficient communication might be made by transmitting and receiving packets in synchronization with the AC power source cycle. FIG. 25 shows an example of a tone map assignment process in a conventional power-line communication. FIG. 25 shows a packet train synchronized with a cycle of an AC power source 1, where a data packet DP and an acknowledgment packet AK are alternately transmitted. FIG. 25 shows a noise level of the power line as a communication medium, where the noise is synchronized with the cycle of the AC power source 1. The system shown in FIG. 25 transmits and receives three packets in synchronization with a half cycle of the AC power source. Data packets DPx, DPy, and DPz having reference signs in a half cycle are packets corresponding to tone maps TMx, TMy, and TMz in accordance with the noise level. For example, the band of packet DPx is 100 Mbps, the band of packet DPy is 20 Mbps, and the band of packet DPz is 10 Mbps. The noise level is greater in the periods of time of packets DPy and DPz. Accordingly, when the tone maps are used to make communication, an error does not occur or is small. A power-line communication technique of grasping characteristics of a communication medium, preparing tone maps, and making map-carrier communication is described in Patent Document 1.
However, the power line is not more stable than other communication lines and has a great variation in characteristics due to connection to electrical instruments and the like. FIG. 26 shows a variation in condition of a power line in the power-line communication system shown in FIG. 25. As shown in FIG. 26, when a range including a great noise level is widened and packets DPx, DPy, and DPz shown in FIG. 26 are transmitted, a noise having a level higher than an assumed level is applied to packet DPz, thereby greatly deteriorating the throughput.
[Patent Document 1] JP-A-2006-333046